A scanning-type image display device is known which irradiates coherent lights (for example white lights) emitted from a white light source such as a halogen lamp, a high-pressure mercury lamp, etc., onto planer display elements such as liquid crystal light valves, etc., and magnifies and projects lights emitted from the display elements on a screen through a projection lens for displaying images.
The aforementioned projection-type image display device is problematic in that a discharge lamp, which is used as a light source, such as a halogen lamp, a high-pressure mercury lamp, etc., requires a measurable amount of power.
By removing out lights of three primary colors of red (R), green (G), and blue (B) with a narrow spectrum width from white lights emitted from the light source, the image display device can achieve a high color reproducibility. However, the problem arises in which the light usage efficiency decreases due to narrowing of the spectrum width, thus darkening the projected image.
By setting wide spectrum widths of respective colors that correspond to the three primary colors for the maximum use of lights from the white light source, light usage efficiency can be increased. However, this decreases the color purity of the three primary colors and this causes a failure to achieve a high color reproducibility. In addition, widening the chromaticity range is also difficult.
Furthermore, since a projection-type image display device having planer display elements such as liquid crystal light valves, etc., inevitably becomes large-scale, miniaturizing the device is difficult.
Furthermore, when the distance from a projection lens to a screen takes a certain value, the image formed by display elements may not be projected within the focal depth of the projection lens, and the projected image may not be in focus. In this case, the user must perform an operation to adjust the focus of the projection lens depending on the distance from the projection lens to the screen. Such an operation to adjust the focus may impair user convenience.
Accordingly, scanning-type image display devices have been proposed wherein a laser light source is used as a light source, and a laser light emitted from the laser light source is two-dimensionally scanned to be projected on a screen for displaying an image (see Patent Document 1, 2).
FIG. 1A shows the configuration of a projection-type image display device described in Patent Document 1.
Referring to FIG. 1A, the projection-type display device comprises light sources 111, 112, 113, color synthesis element 114, collimator lens 115, and light scanning elements 116, 117.
Light source 111 is a red semiconductor laser, light source 112 is a blue semiconductor laser, and light source 113 is a green solid laser. Here, the green solid laser extracts the second harmonic from the emitted light of an infrared semiconductor laser using a nonlinear optical crystal to acquire the green light.
Color synthesis element 114 synthesizes lights of each color of red, blue, and green from light sources 111 to 113. The light flux from color synthesis element 114 enters light scanning elements 116 through collimator lens 115.
Light scanning element 116 performs light scanning in a horizontal direction. Lights from light scanning element 116 enter light scanning element 117. Light scanning element 117 performs light scanning in a vertical direction.
By bringing the position of a beam waist into agreement with a projection plane through collimator lens 115, the above-described projection-type display device is capable of displaying a high-definition image.
FIG. 1B shows the configuration of an image display device described in Patent Document 2.
Referring to FIG. 1B, the image display device comprises light source section 101G, condensing optical system LN1 that condenses light beams from light source section 101G, and reflective mirror 202 that reflects the light beams condensed by condensing optical system LN1 toward screen 110.
Condensing optical system LN1 forms a beam waist at a position which is farther from reflective mirror 202 than from an intermediate position between reflective mirror 202 and screen 110. This reduces the beam diameter on reflective mirror 202, and can also inhibit enlargement of the beam diameter on screen 110. Accordingly, it is possible to miniaturize reflective mirror 202, and to display a high definition image.
In the devices described in the aforementioned Patent documents 1 and 2, a micro mechanical mirror is used as light scanning element 116 and reflective mirror 202.
A micro mechanical mirror described in Patent document 2 will now be described, by way of example.
This micro mechanical mirror comprises a mirror surface, a first substrate on which the mirror surface is fixed through a torsion bar, a second substrate which is arranged opposite to the first substrate, and a core consisting of a magnetic body which is formed on the side of the second substrate that faces the first substrate. The mirror surface is made into a rotary resonant state by an electromagnetic force generated in the core.
As a means for making the mirror surface into a rotary resonant state, an electrostatic actuator and an electromagnetic actuator can be used.